Method of feed-forwardly controlling a tandem rolling mill

ABSTRACT

The thickness of the input material is measured at the entry side of the first roll stand and this value is related to the predetermined desired final thickness of the output material of the mill. The screw down mechanism of the first roll stand and the peripheral speed of the rolls of the first roll stand are then adjusted as a function of the measured and desired final thicknesses to produce an output strip having uniform thickness. The screw down and peripheral roll speeds are adjusted to maintain the incoming volumetric feed rate of the input material substantially constant.

United States Patent Arimura et a1.

[54] METHOD OF FEED-FORWARDLY CONTROLLING A TANDEM ROLLING MILL [72] Inventors: Tohru Arimura; Masamoto Kamata; Morio Saito, all of Kawasaki-shi; Hiromu Suzuki, Chiba-shi; Masakezu Iguchl, Tokyo, all of Japan [73] Assignee: Nippon Kokan Kabishikl Keisha [22] Filed: Nov. 19, 1969 [21] Appl. No.: 877,927

Requlred value of final strip thlcknese 51 July 18,1972

Pn'mary Examiner-Milton S. Mehr Attorney-Flynn & Frishauf 57 ABSTRACT The thickness of the input material is measured at the entry side of the first roll stand and this value is related to the predetermined desired final thickness of the output material of the mill. The screw down mechanism of the first roll stand and the peripheral speed of the rolls of the first roll stand are then adjusted as a function of the measured and desired final thicknesses to produce an output strip having uniform thickness. The screw down and peripheral roll speeds are adjusted to maintain the incoming volumetric feed rate of the input material substantially constant.

10 Claim, 3 Drawing Figures Speed control circuit Variation in roll speed Feed Forward PATENTEUJIUBIQ'IZ 3 577 0 SHEET 1 OF 2 F I6 .I

PRIOR ART NOJSTD N0.2STD NQBSTD NOASTD NO.5STD

3 I X-Ray quuqe v 0 O 0 O Q 4 Speed Reg. Required value of final 6 strip thickness F I G I4 i3 2 l5 NO.lsiand FFAGC -iDeloy AGC strip thickness at I 5 IS I9 delivery side of Deioy screw NO. lstand Down m K CIRCUIT (5% l8 ll 9 7 C5, as-LL A STAND CL- STRIPN Hx V0! m i EI I i LX i I q -i2 Speed control circuit AVI Variation in roll speed Feed Forward METHOD OF FEED-FORWARDLY CONTROLLING A TANDEM ROLLING MILL This invention relates to a method of controlling a tandem rolling mill, such as a cold tandem or a hot tandem rolling mill, by means of preliminarily measuring the thickness of the input material in order to eliminate deviations of the thickness of the material produced.

One prior art control apparatus utilizes a feed-back control system in which the strip thickness is measured after rolling and the rolling mill is then adjusted to produce material of the required thickness.

When such feed-back systems are utilized in a tandem rolling mill, the strip thickness measuring device (or meter) is provided at the delivery side of a rolling stand. The strip thickness is then automatically controlled by feed-back from the meter by adjusting the screw down and/or the roll peripheral speed of the previous rolling stand. The adjustment is a function of the deviation between the strip thickness at the delivery side and the predetermined desired thickness. Accordingly, the speed of response in controlling the strip thickness is very slow due to a time lag from the roll to the thickness measuring device. Moreover, since strip thickness is controlled only after a deviation is detected, the deviation of thickness which initiates the operation of the adjustment mechanism cannot be corrected, and a defective length of material not having the desired thickness will be produced. Moreover, adjusting time in the case of a tandem rolling mill, which is required due to inter-stand interaction, cannot be disregarded. This further increases the amount ofdefective material produced. Increasing the amount of feed-back in order to shorten the adjusting time for a deviation of thickness will result in a greater deviation of thickness due to the well known hunting" phenomenon. The present invention has been developed in order to eliminate the above defects in the prior art.

It is, therefore, an object of this invention to provide an automated rolling system having substantially no time lag in the adjustment process.

Another object of this invention is to provide an automated rolling system having substantially no interstand interaction which would otherwise cause thickness deviations.

SUMMARY OF THE INVENTION In accordance with the present invention, a method of controlling a tandem rolling mill to produce output material having a predetermined desired thickness, comprises the steps of detecting the thickness of the input material at the entry side of the first roll stand of said mill, adjusting the screw down mechanism of the first roll stand as a function of the detected thickness of the input material and as a function of the predetermined thickness of the final output material; and simultaneously adjusting the forward slip rate by adjusting the peripheral speed of the rolls of the first roll stand during the rolling operation, such that the final output material from the rolling mill has the desired thickness.

BRIEF ESCRIPTION OF THE DRAWINGS FIG. I is a schematic drawing of a prior art control system for a tandem rolling mill;

FIG. 2 is a schematic drawing of a feed-forward control system according to the present invention; and

FIG. 3 is a graph illustrating strip thickness variations for the present invention in contrast with the prior FIG. 1 shows a typical prior art feed-back system for a tandem rolling mill. An X-ray thickness meter 2 is located at the delivery side of the roll stand to measure the thickness of the strip produced thereby. When the measured thickness of the strip differs from the desired thickness, the thickness is adjusted to the desired thickness by means of moving the screwdown 3 in the roll-stand. Another X-ray thickness meter 4 is located at the delivery side of the final roll stand 5 (No. 5 stand) where the thickness of strip going out of the final stand 5 is measured. When the measured thickness differs from the desired one, the roll peripheral speed of the roll-stand is altered and inter-stand tension between No. 4 and 5 stands is adjusted by means of roll speed control 6 for the final stand. Thus, the desired strip gauge is obtained. An alternative prior art method of measuring strip thickness comprises detecting the rolling load (p) and indirectly correlating the rolling load to strip thickness from a predetermined relation represented by the equation h Sr+ P/K.

FIG. 2 shows a schematic block diagram of the present invention. A thickness meter 7 is provided at the entry side of the No. I roll stand which comprises rolls 8 anda screw down mechanism 9 coupled to the rolls 8. A thickness meter 10 is provided at the delivery side of the No. 1 roll stand. The screw down mechanism 9 is controlled by a screw down motor ll, and the mill rolls 8 are driven by the driving motor 12 which is controlled by speed control device 17. Signals corresponding to the desired thickness of the strip or sheet is fed by an input device 13 to a thickness control device 14, the output of which is fed to two delay circuits 15. The output of one delay circuit 15 controls motor speed control 17 and the output of the other delay circuit 15 controls the screw down mechanism 9 by means of screw down control circuit 16 and motor 11. An

input device 18 feeds in signals corresponding to the desired value of the thickness of the sheet at the delivery side of the No. 1 roll stand to a control device 19, which compares the desired value with the measured value from meter 10 to further cause the thickness to be controlled by feed-back.

The thickness of the input material is measured by thickness meter 7. This value is fed to control device 14 which relates it with the final desired value to provide an output signal for controlling roll stand No. l to provide the proper output strip. The output of control device 14 is fed, via a delay 15, to control the screw down mechanism 9. When the value of forward slip rate during rolling is not compensated, inter-stand tension between the No. 1 stand and the No. 2 stand (not shown) will vary. This variation is transmitted to the final roll stand and will affect the thickness of output products. Therefore, this inter-stand tension is simultaneously compensated for by altering the roll peripheral speed in No. I stand. Another output of control device 14 is fed to the motor speed control circuit 17 to vary the roll peripheral speed.

Further, the thickness measuring device 10, circuits I8 and 19 and averaging circuit A, provided at the delivery side of the No. 1 roll stand, detect deviations of the outgoing strip thickness as a constant deviation signal. The output of circuit 19 is fed back to adjust the screw down mechanism 9 in No. 1 stand so that the constant deviation may be compensated.

Control circuits 14 and 19 may be special purpose electronic computing circuits or may comprise part of a larger computer. These circuits, and particularly circuit 14, combine values in accordance with a predetermined equation (or equations) to produce an output. Various factors, such as the nature of the material being operated on are taken into account. The particular design of these circuits is dictated by specific system requirements and will vary from system to system. Implementation of such circuits should be apparent to those skilled in the art within the spirit of this invention.

Thus, this invention is characterized by stabilizing the thickness of the outgoing strip and its speed in the No. 1 roll stand by means of a. feed-forward control system. The invention resides in keeping the incoming volumetric speed of strips at a constant value. In a a tandem rolling mill, when the incoming strip thickness changes, incoming volumetric speed is required to be constant in order to keep the strip thickness of the following roll stands at a constant desired value. The following equation applies: U h -v ht-vz (1) wherein:

U is the incoming volumetric speed;

h, is the outgoing strip thickness of the No. 1 roll stand;

v is the outgoing strip speed of the No. 1 roll stand;

hr is the outgoing strip thickness of the final roll stand; and

vi is the strip speed of the final roll stand.

In a control system for deviation of strip thickness at the delivery of No. 1 stand, the following equations apply for the required movement of screw down mechanism 9 and the required change of roll peripheral speed, which corresponding to deviations of thickness of input material.

E i (L-r/ US= 21L AHx e 25 l ASrl 2 wherein the deviation of the input material is represented by A Hx; the amount of movement of the screw down mechanism 9 corresponding to the above deviation, by A Srl; the amount of change of the roll peripheral speed, by A V,; and

H: incoming thickness of the strip h: outgoing thickness of the strip Lx: distance between the first thickness measuring device 7 and the rolls 8 Vol: strip speed of going out of No. 1 roll stand Sr: removing amount of the screw down p: rolling load K: rigidity of the mill v: roll peripheral speed f: forward slip rate S: Lapalcean.

Applying the above equations and 7, the amount of movement ASr of the screw down mechanism 9 and the change of roll peripheral speed AVl, on the basis of a deviation AHx of thickness of the input material can be easily calculated. By using an electronic computer or a computing circuit, there is no difficulty in calculating them.

The numeral l used in the above equations represents the No. 1 stand. The coefiicients (2P/2H) l, (ZflZH) l and forward slip rate fl must be changed by the actual value obtained from the pass schedule during the rolling operation and in this case, of course, the time lag determined by the position of the thickness meter must be taken into consideration.

The graph of FIG. 3 shows the manner in which the strip thickness varies at the delivery side of the No. 1 stand in the present invention, compared with variations present in the conventional feed-back systems of the prior art. In FIG. 3 the dotted line shows the prior art thickness variations and the solid line shows the thickness variations in the present invention. These values were obtained in the case of utilizing an input material having step-like variations of 100 u in thickness.

Thus, according to the present invention, it is possible to completely eliminate the time lag in detecting strip thickness and to eliminate alteration of the inter-stand tension. These improved results are obtained by virtue of the feed-forward control system which adjusts both the screw down mechanism and peripheral speed of the rolls.

This invention is not, of course, limited to the above described embodiment and can also be utilized in a hot tandem mill. In this case the system of this invention must be provided at the entry side of the No. 1 stand to measure both the thickness and the temperature of strip. This information will be fed to a device such as control device 14 which will generate output signals to control operation of the No. 1 stand.

What is claimed is 1. Apparatus for use in a tandem rolling mill during continuous operation thereof to produce output material having a predetermined desired thickness using a feed-forward technique, comprising:

a thickness measuring device located at the entry side of a first roll stand of said mill for measuring the thickness of the input material;

means responsive to said measuring device and to said predetermined thickness of the output material to adjust the screw down mechanism of said first roll stand, and responsive to said measuring device said desired output material thickness and the forward slip rate at said first roll stand to adjust the peripheral speed of the rolls of said first roll stand so that the incoming volumetric freed rate of said input material is substantially constant, and so that the output material from said rolling mill has said predetermined thickness.

2. Apparatus according to claim 1 further comprising:

a second thickness measuring device located at the output side of said first roll stand for measuring the thickness of the output material from said first roll stand;

means indicating the desired thickness of the output material from said first roll stand; and

means responsive to said second measuring device and to said indicating means to further adjust said screw down mechanism and said peripheral speed of said rolls by feed back.

3. A feed-forward method for continuously controlling a tandem rolling mill during continuous operation thereof to produce output material having a predetermined desired thickness, comprising the steps of:

detecting the thickness of the input material at the entry side of a first roll stand of said mill during the rolling operation,

adjusting the screw down mechanism of said first roll stand during said rolling operation as a function of the detected thickness of the input material to said first roll stand and as a function of said predetermined thickness of the final output material; and

simultaneously adjusting the peripheral speed of the rolls of said first roll stand during said rolling operation as a function of the forward slip rate for said detected thickness, to cause the final output material from said rolling mill to have said predetermined desired thickness.

4. A method according to claim 3 wherein the peripheral speed of said rolls is adjusted additionally as a function of said detected and predetermined final thicknesses of said material.

5 A method according to claim 3 wherein said screw down mechanism and roll peripheral speed are adjusted to maintain the incoming volumetric feed rate of said input material substantially constant.

6. A method according to claim 3 further comprising the steps of:

detecting the thickness of the material at the output of said first roll stand; comparing the detected output thickness with the desired thickness of the output material of said first stand; and further adjusting said screw down mechanism as a function of said comparison by feed back.

7. A method according to claim 3 comprising delaying adjusting of the screw down mechanism of said first roll for a predetermined period of time substantially corresponding to the amount of time required for the strip to pass from the point of thickness detection to the first roll stand.

8. A method according to claim 3 comprising delaying adjusting the peripheral speed of the rolls of the first stand for a predetermined period of time substantially corresponding to the amount of time required for the strip to pass from the point of thickness detection to the first roll stand.

9. Apparatus according to claim 1 wherein said adjusting means includes first delay means for delaying adjustment of said screw down mechanism of said first roll by a time corresponding to the amount of time required for the strip to pass from the point of thickness detection to the first roll stand.

10. Apparatus according to claim 1 wherein said adjusting means includes a second delay for delaying adjusting of said peripheral speed of said rolls of said first stand by a predetermined time which substantially corresponds to the amount of time required for the strip to pass from the point of thickness detection to the first roll stand.

l l I i i 

1. Apparatus for use in a tandem rolling mill during continuous operation thereof to produce output material having a predetermined desired thickness using a feed-forward technique, comprising: a thickness measuring device located at the entry side of a first roll stand of said mill for measuring the thickness of the input material; means responsive to said measuring device and to said predetermined thickness of the output material to adjust the screw down mechanism of said first roll stand, and responsive to said measuring device said desired output material thickness and the forward slip rate at said first roll stand to adjust the peripheral speed of the rolls of said first roll stand so that the incoming volumetric freed rate of said input material is substantially constant, and so that the output material from said rolling mill has said predetermined thickness.
 2. Apparatus according to claim 1 further comprising: a second thickness measuring device located at the output side of said first roll stand for measuring the thickness of the output material from said first roll stand; means indicating the desired thickness of the output material from said first roll stand; and means responsive to said second measuring device and to said indicating means to further adjust said screw down mechanism and said peripheral speed of said rolls by feed back.
 3. A feed-forward method for continuously controlling a tandem rolling mill during continuous operation thereof to produce output material having a predetermined desired thickness, comprising the steps of: detecting the thickness of the input material at the entry side of a first roll stand of said mill during the rolling operation; adjusting the screw down mechanism of said first roll stand during said rolling operation as a function of the detected thickness of the input material to said first roll stand and as a function of said predetermined thickness of the final output material; and simultaneously adjusting the peripheral speed of the rolls of said first roll stand during said rolling operation as a function of the forward slip rate for said detected thickness, to cause the final output material from said rolling mill to have said predetermined desired thickness.
 4. A method according to claim 3 wherein the peripheral speed of said rolls is adjusted additionally as a function of said detected and predetermined final thicknesses of said material.
 5. A method according to claim 3 wherein said screw down mechanism and roll peripheral speed are adjusted to maintain the incoming volumetric feed rate of said input material substantially constant.
 6. A method according to claim 3 further comprising the steps of: detecting the thickness of the material at the output of said first roll stand; comparing the detected output thickness with the desired thickness of the output mateRial of said first stand; and further adjusting said screw down mechanism as a function of said comparison by feed back.
 7. A method according to claim 3 comprising delaying adjusting of the screw down mechanism of said first roll for a predetermined period of time substantially corresponding to the amount of time required for the strip to pass from the point of thickness detection to the first roll stand.
 8. A method according to claim 3 comprising delaying adjusting the peripheral speed of the rolls of the first stand for a predetermined period of time substantially corresponding to the amount of time required for the strip to pass from the point of thickness detection to the first roll stand.
 9. Apparatus according to claim 1 wherein said adjusting means includes first delay means for delaying adjustment of said screw down mechanism of said first roll by a time corresponding to the amount of time required for the strip to pass from the point of thickness detection to the first roll stand.
 10. Apparatus according to claim 1 wherein said adjusting means includes a second delay for delaying adjusting of said peripheral speed of said rolls of said first stand by a predetermined time which substantially corresponds to the amount of time required for the strip to pass from the point of thickness detection to the first roll stand. 